(a) Technical Field
The present disclosure relates generally to an apparatus and a method for pre-heating an engine of a mild hybrid vehicle, and more particularly, to an apparatus and a method for pre-heating an engine of a mild hybrid vehicle, which control a pre-heating period differently according to a coasting driving period.
(b) Description of the Related Art
In general, various types of engines exist including a gasoline engine and a diesel engine. The gasoline engine is an internal combustion engine using gasoline as a fuel, sucks air and gasoline into a cylinder, and then ignites and combusts the compressed mixed gas. The diesel engine is an internal combustion engine using diesel as a fuel, sucks air into the cylinder, compresses the sucked air at a high pressure with a piston, injects the fuel at a high temperature and a high pressure, and then combusts the injected fuel by autoignition.
Since the diesel engine has higher thermal efficiency than the gasoline engine, fuel consumption is low, and as a result, the diesel engine is more economical. Therefore, in some instances, the diesel engine has been applied to a hybrid vehicle instead of the gasoline engine. A pre-heating plug (i.e., glow plug) that increases combustion performance by pre-heating air in an engine combustion chamber while cold starting can be mounted on the diesel engine.
In a typical diesel engine vehicle, since the engine does not stop while driving after starting, the pre-heating plug is used only during initial starting. Further, even in the case of the diesel engine vehicle to which idle stop and go (ISG) is applied, since the engine idle-stops only when the temperature of the engine is equal to or higher than a predetermined temperature, the pre-heating plug is used only during the initial starting.
On the contrary, in a hybrid vehicle with the diesel engine, the engine is frequently turned on/off together with driving of a motor. Accordingly, the pre-heating plug needs to be used whenever the temperature of the combustion chamber is low while starting the engine.
Meanwhile, a hybrid vehicle uses the engine and the motor as a power source. Hybrid vehicles include a hard type and a mild type. The hard type is a type that separately includes a drive motor for driving the vehicle and a generator producing power for actuating the drive motor; the mild type is a type configured in such a manner that one motor serves as both the drive motor and the generator.
FIG. 1 is a diagram illustrated for describing coasting driving of a mild hybrid vehicle. As shown in FIG. 1, the mild hybrid vehicle generally enters a coasting driving mode in which the mild hybrid vehicle is driven by inertia of the vehicle for fuel saving when a driver does not step on deceleration and acceleration pedals. For example, the vehicle enters the coasting driving mode during intervals A, B, and C when a vehicle velocity decreases. During the coasting driving mode, a clutch connecting the engine and the drive motor is controlled in a release state and the engine is switched to an off state. Further, the vehicle enters a fuel cut state in which fuel injection into the engine is cut.
Accordingly, as the temperature of a combustion chamber of the engine is lowered during the coasting driving mode, and the coasting driving mode ends, when the engine is switched to an on state again, combustion stability of the engine deteriorates. Therefore, in a mild hybrid vehicle, the engine is pre-heated through the pre-heating plug whenever the coasting driving mode ends. However, even when the coasting driving interval (A) is relatively shorter than driving intervals (B) and (C), pre-heating periods are the same as each other, and as a result, the temperature in the combustion chamber is higher than a target temperature and battery voltage for heating the pre-heating plug is unnecessarily consumed.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the disclosure, and therefore it may contain information that does not form the related art that is already known in this country to a person of ordinary skill in the art.